Some electric motors are used in actuators that provide motion between a first position and a second position. For example, an actuator may be coupled to a spring that biases it to a first position. An electric motor for the actuator may activate and move the actuator to a second position against the spring bias. Once the second position is reached, it is often desirable to stop further actuation while holding the actuator in the second position. Continuing to operate the electric motor at full power with the actuator against, for example, a physical stop, may cause wear on various components of an actuator system. Instead, in some systems, a lower power Hold state is used to keep the actuator in the second position. In the Hold state, the electric motor exerts sufficient force to keep the actuated device in its desired position without excessively straining the actuated piece. The inclusion of a Hold state may also reduce power consumption and associated heat.
Some designs may encounter problems, however, when power to the actuator system is less than ideal (e.g. interrupted or lower than expected). For example, when power turn-on occurs slowly, analog latching circuitry may fail to enter the correct post-turn-on state. The result can be that the motor enters a Hold state, rather than the run state.
For another example, a power interruption may allow motion of the actuator away from a desired position while also causing the actuator system to enter or remain in the Hold state once power is restored. If this occurs, the actuator will not be in its desired position and, since the Hold state occurs, the actuator will remain in this incorrect position. It would be useful to prevent and/or remedy such circumstances.